This invention relates in general to an electrode apparatus for dialysis of a liquid, and, more particularly, to an electrode apparatus for dialysis which is completely submergible below the surface level of a fluid in a container.
Electrodeposition is a process by which coatings are applied to the surface of an object by the action of an electrical current. The process utilizes an electrodeposition tank or bath filled with a cationic or anionic solution containing a coating to be deposited onto an object, with the coating having a known degree of ionization allowing it to be affected by an electrical current. The object to be coated, or substrate, is placed into the solution into the tank and a source of electrical current is connected thereto. An electrode-type device is then introduced into the solution in spaced relationship from the substrate and serves as an oppositely charged counterelectrode to the substrate. The electrical forces thus created cause the coating to be attracted to and thereby deposited onto the substrate.
In both anionic and cationic electrocoating processes, it is often necessary to add a neutralizer, i.e. an alkali or an acid, to the ionic coating solution in order to adjust the electroconductivity thereof. An ion exchanger or electrodialysis membrane is used as part of the electrode apparatus to separate the counter-electrode from the solution within the electrodeposition tank, and excess alkali or acid within the solution is then dialyzed and removed therefrom through the membrane.
An electrode device commonly utilized for these electrocoating or electrodeposition applications serves as both a counterpart electrode for the object which is to be coated or painted, and as a dialysis device for the removal of excess neutralizer from the solution. In these devices, the electrode is separated from the solution by a membrane generally surrounding at least a portion of the electrode and through which the neutralizer flows. A space is provided within the device between the membrane and the electrode for accumulation of the neutralizer during filtration. During the electrodeposition coating process, the charged electrode of this dialysis-type device provides direction to the coating. The opposite electrical charge provided to the substrate attracts the coating thereto, and the coating is thereby deposited onto the substrate. An ion exchanger or electrodialysis membrane barrier is provided within the device to prevent the passage of any metal ions from the electrode into the electrodeposition tank during this process, but allow for the passage of the neutralizer filtrate from the solution into the device.
It is necessary to remove the excess neutralizer from the solution because the concentration of the neutralizer increases as electrodeposition occurs. Neutralizer that passes through the membrane barrier is flushed from the area between the electrode and the membrane by an anolyte fluid. This anolyte fluid enters the device and flows first through the electrode, and then through the area between the electrode and the membrane. As the anolyte solution flows within the electrode device, it accumulates any excess neutralizer which has been drawn through the membrane by the charge of the electrode. The anolyte and filtrate mixture is removed from the device through an anolyte discharge port.
The electrode devices used in electrodeposition processes have traditionally been positioned in the electrodeposition tank in such a manner that the electrical connections serving to supply the charge to the electrode are retained above the fluid level of the aqueous solution in the tank. More recently, submergible electrode devices have been developed which can be positioned within the electrodeposition tank completely below the fluid level of the electrodeposition solution therein. One problem that occurs with these submergible devices is that the electrical connection within the devices are exposed to the fluids which are involved in the electrodeposition process. Such exposure can produce corrosion of the wiring or electrode, with resultant failure of the electrode cell due to breakage of the electrical connection.
In order to remedy this problem, the electrical connection in submergible electrode devices is conventionally protected by one of two primary methods. First, the electrical connection of the electrode can be permanently sealed using a type of sealing material such as glass fiber and epoxy potting. This method contemplates continued placement of the electrical connection within the fluid stream in a permanent seal which protects it from the fluid stream. The second conventional method permanently pots the entire interface surrounding the electrical connection in an epoxy slug to completely insulate it from the fluid stream. Both of these methods, however, are extremely labor and cost intensive. In addition, as the electrical connection is permanently potted or insulated, the entire electrical connection must be replaced and repotted in a labor intensive process whenever maintenance on the connection is required.